Generally, ink-jet recording is performed with an ink set comprising three colors of ink, namely a yellow ink, a magenta ink, and a cyan ink. A color image is formed by applying the three colors of ink to a substrate. Further, in the ink-jet recording, a black color (composite black) is formed by a mixing or an overstriking of the yellow ink, the magenta ink, and the cyan ink. Images formed by the ink-jet recording are prone to color deterioration over time. Due to the deterioration of the color, a color balance of the image may be changed from that of initial image shortly after recording. One proposal to address the problem of the color deterioration has been to provide an ink set which controls ΔE (color difference) in L*a*b* calorimetric system before and after a light resistance test, and also a reflection density residual ratio. The ink set is a combination of inks whose ΔE is 10 or less and reflection density residual ratio is at least 70%.
However, the images formed using such ink sets are prone to ozone degradation. Further, the ink set is focused on the deterioration of individual ink colors. Therefore, the ink set does not solve the problem of a color deterioration balance among images formed by inks of different colors. In addition, composite black images may occasionally become colored over time due to uneven deterioration of the individual color inks. The color generated because of the deterioration of the composite black is more readily visible than a change of a color in a color image.